Method for vacuum dehydration

ABSTRACT

A method and apparatus for the dehydration of products where the products are placed in a cell comprising electrically conductive transverse heating plates uniformly spaced by conductive spacers, the plates being connected in parallel and uniformly conductive over their entire surfaces; said plates being the only heating source. The filled cells are placed in individual carriers. One or more such carriers are treated in separately controlled chambers under high vacuum of the order of 100 to 1000 microns of mercury with rapid withdrawal of water vapor and in which a single source of electrical power under external control is connected to each cell for the simultaneous and uniform heating of each plate of each cell.

United States Patent 1 Van Gelder June 11, 1974 METHOD FOR VACUUM DEHYDRATION Arthur Van Gelder, 409 W. Aliso St., Ojai, Calif. 93023 22 Filed: Mar. 10,1972

[211 App]. No.: 235,450

[76] Inventor:

52 US. c1; 34/5, 34/92 [51] Int. Cl. F26b 5/06 [58] Field of Search 34/5, 92

[56] References Cited UNITED STATES PATENTS 3,39l,466 7/1968 Brouwer et al, 34/5 Primary Examiner-William F. ODea Assistant ExaminerWilliam C. Anderson [5 7 ABSTRACT A method and apparatus for the dehydration of products where the products are placed. in a cell comprising electrically conductive transverse heating plates uniformly spaced by conductive spacers, the plates being connected in parallel and uniformly conductive over their entire surfaces; said plates being the only heating source. The filled cells are placed in individual carriers. One or more such carriers are treated in separately controlled chambers under high vacuum of the order of 100 to 1000 microns of mercury with rapid withdrawal of water vapor and in which a single source of electrical power under external control is connected to each cell for the simultaneous and uniform heating of each plate of each cell.

6 Claims, 10 Drawing Figures PATENTEDJUH n 1924 3815251 SHEET 10$ 5 PATENTEBJUN 1 1 mm 3.815251 SHEETBOF 5 FIEr 7 93 91 PATENTEU JUH l 1 I974 SHEET 5 OF 5 M W M W W W 7 f FM 6 w m N I? L Z L 1. L EF. Ll. n 0 D L EL L U O 6 An N L F C U F F. m H .K Y M 0 6 L F RFOIUO 5 E DA N MT A CLDAN 9 CLO T Hmfu 1 METHOD FOR VACUUM DEHYDRATION BRIEF DESCRIPTION OF THE INVENTION The plates for the cells are preferably arranged transversely vertical with respect to the longitudinal axis, each plate being a laminate consisting of an electrical resistance element of a carbon coated plastic capable of conducting electrical current uniformly over the entire area having electrodes in contact with electrical conductors along the longitudinal margins of the plate. The heating or electrical resistance material is specially selected to produce about 2 watts per square inch or about 6.836 BTU per square inch. The wattage is the controlling factor and if confined to about 2 watts the laminate provides its equivalent in heat sufficient to accomplish the optimum result.

The material to be dehydrated may be liquid, semisolid or solid. If it is aliquid it must be pretreated to a snow-like frozen state. If the material is a semi-solid of sufficient integrity, it may be inserted between the plates without pretreatment. If the material is a solid it may be placed between the plates either in pre-frozen state or in a fresh state where it is immediately frozen by evaporative freezing in the high vacuum.

The products in the cells are submitted to controlled heat by means of the current passing through the plates producing heat, under a high vacuum of the range of 100 to 1,000 microns of mercury, providing sufficient differential vapor pressure between the product and its environment to allow the withdrawal of water vapor in a substantial volumeat a high rate. In-this manner the product is dehydrated quickly to a low moisture content of the range of 1 percent to 4 percent.

BACKGROUND OF INVENTION The present invention is fundamentally the discovery that the plates of the cell can be constructed individually so that each will have substantially the same heating characteristics to provide the heat for evaporation and dehydration. It was found unexpectedly and surprisingly that when the current for each plate was confined to from onetenth to 2 watts, it produced the equivalent in heatin every other plate. Furthermore when plates of the cell are connected in parallel the heating became uniform not only for each cell but for every other cell in the same carrier so that each of the cells in the same carrier would have the same uniform heat.

Dehydration had formerly been accomplished in a tube with carriers inserted in the tube and under high vacuum with rapid withdrawal of the vapor, using induction heating. This method and apparatus required a very careful and knowledgable winding of the induction coils and eleaborate external controls to accomplish the heating. This all has been eliminated and the results obtained by the present method and structure appear to be superior in all respects as well as being considerably less expensive per pound of product produced and more adaptable to commercial practices.

CROSS REFERENCE TO RELATED INVENTION under Ser. No. 664,186 and issued as US. Pat. No.

3,455,031 on July 15, 1969.

Further objects are to provide a construction of maximum simplicity, economy and ease of assembly and disassembly, also such further objects, advantages and capabilities as will fully appear and as are inherently possessed by the device and invention described herein.

The invention further resides in the combination, construction and arrangement of parts illustrated in the accompanying drawings, and while there is shown therein a preferred embodiment thereof, it is to be understood that the same is illustrative of the invention and that the invention is capable, of modification and change and comprehends other details of construction without departing from the spirit thereof or the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS In thedrawings:

FIG. 1 is a perspective explodedview showing the portions for the assembly of a plate with acompleted plate at the left.

FIG. 2 is an enlarged cross section of a completed plate taken on the line II II of FIG. 1 and showing the electrical connectionfor each plate together with the spacers involved;

FIG. 3 is a fragmentary vertical side elevational view of the plate making up an individual cell.

FIG. 4 is an expanded perspective view of a complete cell and its shield showing the manner of inserting the cell into its shield to make a unitary assemblage.

FIG. 5 is an end view partly in section, taken on the line V V of FIG. 4 showing the cell inposition in its shield and the electrical connections for each cell.

FIG. 6 is a fragmentary vertical section on an enlarged scale taken on the line VI VI of FIG. 4.

FIG. 7 is a perspective view showing the individual cells in their respective shields loaded within a carrier in vertical fashion and being lowered into position in a treating chamber. The main source of current is shown at the bottom of the chamber. I

FIG. 8 is a vertical fragmentary section taken substantially on the line VIIl VIII of FIG. 7 but with the carrier lowered into position within the treating chamber.

FIG. 9 is a vertical longitudinal section taken on the line IX IX of FIG. 8 showing thecontact to the main source of electrical power, and

FIG. 10 is a flow sheet for the operation of this method.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings :in which like reference numerals are used to identify like parts throughout the drawings and this description, reference will first be made to FIGS. 1, 2, 3 and 4. Since the cell is the controlling unit for this method and apparatus it will be generally designated as 20. The basic unit in each cell 20 is the heating plate structure generally designated 21.

The structure of the plate 21 is a laminated assembly which can best be described by reference to FIG. 1. The primary element of the plate 21 is the sheet 22 of a carbon coated plastic which is relatively thin and flexible. This is preferably the duPont product known commercially as Pyraline which has high dielectric characteristics and is a conductor having approximately eighteen ohms resistance per square inch uniformly over the entire area. This product has unusual characteristics in that it withstands temperatures up to 600F. and can be coated with plastics without altering its resistance characteristics in any substantial degree. Each sheet 22 is provided with two electrodes which are showing in FIG. 1, with electrode 23 at the top and electrode 24 at the bottom. These electrodes can be preferably copper but any suitable conductor is serviceable for this purpose. Each electrode is secured in any suitable manner to the electrically resistant material 22 to make certain that the contact is substantially uniform for the entire distance. Since the suggested operation of the electrical current is applied through the electrodes 23 and 24 to the resistant material 22 is 25 volt operation two benefits are immediately obtained. The first is that the 25 volt operation does not require the safety regulations and precautions required of higher voltages. Secondly, this voltage determines the distance between electrode 23 and electrode 24. At this voltage operation the spacing the electrodes 23 and 24 four inches apart provides the operating characteristics of two watts per square inch. The control therefore, for the heating is from one-tenth to 2 watts per square inch. The arrangement described herein provides a convenient size and weight for the plates and the cells. On either face of the sheet 22 are plastic insulating sheets 26 and 27 which have a twofold function in both insulating and unifying the laminate into a unitary structure. The sheets 26 and 27 are narrower than the sheet 22 exposing the copper electrode above and below the gripping portion which is numbered 28. The whole assembly is then covered by epoxy adhesive material and then are in turn covered by the outer metal plates 30 and 31, which are complimentary, and made of etched aluminum to preserve the high conductivity of the heat involved. It is also apparent that the laminate with these metal plates 30 and 31 will make a plate of high rigidity which is most desirable. It will be observed that at the longitudinal margins of the laminate the plate 30 hooking over at the top does not meet or engage the upper edge of the plate 31. Also, the plate 31 hooking under and upwardly in the laminate will not meet themarginal edge 33 of the plate 30. The space in between, approximately one-sixteen inch, leaves a space which is insulated to keep any short-circuiting between the two poles. This gap is shown on the plate in FIGS. 1, 2 and 3 as 34 on one side and 35 on the other side. While the epoxy glue is still wet the completed assembly is pressed into a complete unitary structure leaving, of course, the gap 34 and 35 as described. Each completed plate 21 has suitable holes passing through the electrodes at either side for contact with the electrical energy source. These holes are identified as 36, 37, 38 and 39.

While the number of plates to each cell may vary according to the predetermined spacing, the particular cells shown have 108 plates 21 of a size of about 6 inches high and 12 inches wide and spaced threeeighths of an inch apart. Each cell will contain in use therefore approximately 50 to 60 pounds of product.

In FIG. 3 there is shown the manner of spacing and securing the electrical contact for the electrodes of each plate. The spacer for the plates is shown at 40 and has a hollow bore 41 longitudinally therethrough and an inner recessed portion or counter bore 42. The narrow end 43 of the spacer 40 is tapered as shown in FIG. 3. The tapered portion 43 passes through the openings 36 39 and is expanded into the opening 42'of the adjacent spacer 40. This is also shown in FIG. 2. The spacers themselves are aluminum and therefore conductive of the electric current. In assembling the plates in the cell with the spacers 40 it will be observed that the spacers at either side engage the copper electrodes 23 and 24. When assembled they appear as shown from the top plan view infra'gment of FIG. 3.

The complete assembly of the cell 20 with its numerous plates 21 is shown at best in FIG. 4. v

In the final assembly at either end of the cells on the tie rods 44 to 47 inclusive, the whole assembly is cinched up by the nuts 48 to each end with lateral conducting tie rods 51 to 53 at either end. The tie rods at one end are provided with connector prongs, prong number 54 being on tie electrical conductor 52 and prong number 55 being on conducting tie rod 53. This is also shown in FIG. 6. On the vertical edges of each plate 21 at either side are placed the U-shaped Teflon protector 56. These are to prevent electrical short circuit, as will be described later. The cell is then dropped into a shield generally designated 57. The shield 57 is a box-like structure with its longitudinal side walls 58 and 60 vertically higher than the end walls 61 and 62. The end walls are cut lower so that when the cell is dropped into position within the shield 57 the connector rods 50 and 52 will not make contact. The shield itself is preferably made of aluminum which is perforated as exemplified at 63. It is perforated on all four sides and at the bottom in order to allow the rapid escape of vapors and to hold in the material during the process. All of the plates of the cell rest on the bottom of the shield 57 and the whole cell and shield are made into a unit by the tie rods passing through the holes 64 and then tightened by the nut 48. The positioning of the connector bars with respect to the shield is different at the forward end from those at the rearward end, i.e., 53 and 52 are on the outside of the shield so that the connector prongs 54 and 55 are available for connection to the main source of power. This is shown particularly in FIG. 6. As will be observed in FIG. 6 the Teflon edge protecting members 56 prevent contact of the plates 21 with the sidewall 60 of the shield 57. It will be observed that this attachment of the cell in the shield grounds one pole of each and every plate 21, as the whole system is grounded by the-shield. The exterior bottom surface of the shield is provided with two longitudinal runners 65 the purpose of which will be described later. Also the forward end of the shield has a handle grip 66 which is fastened between and on the protruding ends of the tie rods 44 and 45 through the holes 64. This handle gives additional rigidity to the unit and greatly simplifies the loading and minimizes damage in the handling.

As will be observed from FIG. 4 when the cell 20 is secured within the shield 57, the cutbacks of the forward wall 61 and the rear wall 62 prevent any possible contacts with the conductor bars 50 and 52 of the cell.

the carrying of nine units, cells and shields, in a vertical t or tiered arrangement. Obviously any suitable number of cells and shieldsrnay be used, but nine is the number which is described at this point.

The frame of the carrier 71 is an open framework with four vertical posts 72, one at each corner, connected at each end with a transverse member 73 at each level and longitudinal members 74 also at each level the latter members being arranged in accordance with the predetermined height of the shield 57 plus the runners 65 and plus space for vapor passage. There are in additional longitudinal bars 75 at each level directly beneath the runners'65. On top of the longitudinal bars 75 are parallel channels 76 for receiving the blade of the runners 65. The channels are lined with Teflon for easy running and sliding of the runners 65 with no wear or maintenance involved.

At the rear of the frame of the carrier 72 are two parallel electrical conducting bars 77 and 78, arranged vertically from below the bottom level to the topmost level. They contain female sockets 80 and 81 to receive respectively the male prongs or connectors 54 and 55, 54 being received in the socket 81 and 55 in the socket 80. At thelower end of each connecting bar 77 and 78 there is an L- shaped offset 82 and 83 respectively connected to parallel longitudinal bars 84 and 85. The under surface of the bars 84 and 85 have a V-shaped inward cut or groove 86 and 87. The grooves 86 and 87 have two main purposes. First, they position the carrier within the'treating' chamber in the precise position, and second, they provide a continuous longitudinal extended surface of contact as an electrical conductor.

It will be noted that the corner posts of the carrier frame 72 do not touch the bottom of the treating chamber 70. This is clearly shown in FIG. 8. Accordingly, the whole weight of the carrier and its content is born by the .V-shaped contact 86 and 87. In order to support this weight properly and evenly the space between the lowermost transverse bars 73 and the upper surface of the longitudinal bars 84 and 85 is filled with insulating spacers 88. As shown in FIG. 9 the connectors 80 and 81 have spring or other suitable means 90, to make the full contact certain over the distance of the engagement.

Referring again to FIG. 7, at the bottom of the treating chamber 70 there are parallel longitudinal conductor bars 91 and 92-. The upper surface of these parallel bars is formed into an upwardly extending V-shape 93 and 94 continuously to engage in V-shaped slots 86 and 87 of the carrier. Since these bars are designed to carry a maximum of 4,000 amperes they are insulated from the bottom of the chamber 70 by the continuous insulation bars 95. The current is brought to the apparatus by the parallel cables 96 which pass through the end wall of the chamber 70 with vacuum type sealers shown as 97. The cable is directly connected to the conductive bars 91 and 92 through the conductor rod 98.

A sufficient open space is provided around the carrier within the chamber 70 to provide rapid withdrawal of water vapor during treatment, in the large volume required for this operation. In order to provide for the escape of the water vapor released by the vacuum within the chamber, the release is secured through the large openings100 which are in turn connected to the main operating manifold and condensors (not shown). Obviously in order to provide the proper operation of the treating chamber 70, a valve is supplied in this line so that the vacuum and withdrawal of vapors can be closed off except when the treatment is under operation. A topor hinged cover 101 is providedso that the carrier and its load of cells can be lowered into position within the chamber. During the operation the cover 101 is closed and sealed vacuum tight to make the chamber hold the vacuum during the treatment.

OPERATION OF THE METHOD To initiate the operation of the apparatus and perform the steps of the method disclosed herein the material to be treated undergoes some pretreating conditioning depending upon the nature of the product. For example, if the product tobe treated is a liquid or liquid with solids up to 22 percent the material is prepared by evaporative freezing to a s now-like condition of porous particles of approximately peasize or less. If the mate rial to be treated is a liquid containing solids above 22 percent then'the starting material is belt-frozen and the resulting frozen sheet material particulate d to a powder or granulated frozen state. If the material to be treated is a solid it may be pretreated in one of two ways. Either it can be frozen and then sliced into the thicknesses required for the cells or, it can be preshaped in its fresh state and loaded into the cells where it is evaporatively frozen as part of the dehydration process.

The steps in carrying out the process have been arranged in the flow sheet which is FIG. 10. Any pre frozen or preconditioned material in the frozen state is delivered to a fluidized bed freezer 110 of conventional manufacture which has an air temperature of approximately 40F. The effect is to standardize the tempe rature of the products at the time of loading into the cells.

From the fluidized bed freezer 110 the material is delivered to a vibrating cell loader 111. By using'this equipment in the loading of the cells, the snow-like or frozen material is compacted within the space between the plates of each cell. The material cannot escape from the space between the plates because the shield 57 is holding the same in position at the sides and at the bottom so that the compaction insures a full cell load- For purposes of control and indicating temperatures, a thermocouple or thermist'er is embeded in a specified plate of each cell. This is connected for operation at the time the cells and their shields are loaded into the carrier. This loading operation is illustrated by the box 112. Obviously, at this point if a chamber is not available for treatment of the material at the particular time, the loaded carrier can go into a carrier holding freezer 114 which maintains the temperature uniformily at all times. It should be pointedout that at the time the cells 20 are loaded into the carrier 71, as they are loaded at each level, the electrical connections required for the operation are engaged immediately. The pushing of the cell and its shield into position within the carrier at any one level will accomplish this electrical connection. The loaded carrier with all its electrical connections intact is then lowered into the treating chamber 70 until the longitudinal V-slots 86 and 87 of the. carrier engage theV-shaped contact 93 and 94 within the chamber. As stated earlier, this V-shaped contact positions the carrier 71 precisely within the treating chamber 70 and provides for electrical surface contact over the full length of the bars 91 and 92. When the carrier is positioned within the treating chamber 70 the multiple thermocouple control coupling for the cells is attached and the cover 101 of the chamber 70 is lowered and sealed; Up to this point the vacuum tight valve 115 has been closed so as not to dissipate or waste power in a non-vacuum tight situation. When the chamber 70 has been loaded, the valve 115 may be opened subjecting the interior of the chamber 70 to the immediate and large volume withdrawal of water vapor and high vacuum which is the function of the vapor condenser 116 and the vacuum pump 117. Obviously the time required drawing the operating high vacuum of from 100 to 1,000 microns of mercury, can be reduced in the conventional manner of a preliminary partial vacuum being established before the big valve 115 is opened.

At the same time the source of electric power 112* with its transformer 120 and the controlling mechanism 121 are initiated so that the energy is connected through the cables 96 to the bars 91 and 92 then through vertical conductors 77 and 78 on the carrier, through the connections of the prongs 54 and 55 and their couplings 80 and 81 to each individual plate in the cell, in the manner heretofore indicated. The thermocouple controlled mechanism provides a constant proportionally controlled heat energy to the plates of the cell sufficient to provide for maximum evaporation without melting the frozen product. In other words, the control of the heat requirement is in accordance with the requirements of the product itself undergoing the treatment. Also as stated earlier, because of the nature of the electrical connections and the structure of the individual plates, the temperature is uniform for each plate of every cell and for each cell in the entire tier of a single carrier 71. In this manner uniformity of result is insured.

At the conclusion of the treatment the valve 115 is shut and substantially atmospheric pressure is restored by means of a bleeder valve which is not shown. At the conclusion of this phase the cover or lid 101 of the chamber is opened and the loaded cell carrier 71 with the treated cells is removed by means of a cell carrier conveyor 122. The carrier with its cells and finished product are taken to a cell unloader 123 which operates at normal room temperatures and atmospheric pressure without damage to or alteration of the product, where by means of an air jet the product is released from the space between the plates for packaging, storing or other purposes.

It is to be noted that in accordance with conventional practice, the plates of the vapor condenser 116 should always be colder than the product ungergoing treatment. It is, of course, obvious that the temperature of the vapor condenser plate is directly related to the vacuum drawn in the treating chamber 70.

In this process or method the maximum power use over a two hour period, using, for example one cell of frozen coffee extract containing percent solids and a total weight of 60 pounds of ice, 85 percent of water or 38.25 pounds of water is removed. The electric power consumption is 7.44 KW hours which is equivalent to 2.543 million B.T.U. The calculated requirement being about 1,200 BTU. per pound of water removed would be a total of 4,590 million B.T.U. in this example the sensible heat input is approximately only 55 percent of that calculated requirement. Each product has its own characteristics and the percentage varres.

However, on an average the sensible heat input is approximately one-third of that required to accomplish the evaporated dehydration of this method. It is believed that the remaining two-thirds of the heat requirement is provided by the product itself undergoing the treatment. The theoretical explanation of this is thought to be the very high molecular velocity involved in the removal of the water vapor by this method which produces the remaining heat requirements, possibly through molecular friction. However, whatever the explanation may be the fact remains that the electrical heat input is only one-third of that calculated to be the required for the total heat requirement for the evaporation dehydration of the product to the range specified herein.

I claim:

1. The method of vacuum dehydration, the steps of providing cell carriers for receiving the material to be dehydrated said cell carriers having a plurality of spaced vertical transverse electrically conductive and resistive rigid plates which when energized become the heat source with electrically conductive spacers therebetween, producing a controlled source of heat uniformly over the entire surface of each plate and uniformly with respect to all other plates of said cell carrier, loading the material to be dehydrated in said cell carrier between the plates and in contact therewith, placing and sealing the loaded cell carrier in a vacuum chamber, establishing a vacuum of to 1,000 microns of mercury in said chamber, and simultaneously removing the water vapor at an accelerated rate while passing an electric current through the said cell plates to provide a heat source uniformly over the entire surfaces of each plate of the cell carrier.

2. The method of claim 1 wherein the heating is controlledby establishing an electrical resistance in the plates to produce an electrical heat source of less than 3 watts per square inch with an input of 25 volts uniformly over both surfaces of each vertical plate, to reduce the water content in the material to be dehydrated to l to 4 percent in the final product.

3. The method of 'claim 1 wherein a plurality of loaded cell carriers are placed in a single chamber, and wherein all cell carriers are connected to a single source of controlled electric power when positioned within said chamber, and energizing said plates for a uniform heating source with respect to both surfaces of all plates simultaneously and continuously.

4. The method of claim 1 wherein the heating source plates of each cell carrier are connected in parallel so that when the loaded cell carriers are connected to a single source of controlled electric power the heating source is simultaneous and uniform over the entire plate areas for each plate in each of the cell carriers.

5. The method of claim 1 wherein the sensible heat input of the heat source plates is less than the calculated requirements to accomplish dehydration in the product to a water content of l to 5 percent.

6. The method of claim 1 wherein the plurality of loaded cell carriers are arranged in a second carrier for transportation to, treatment in, and removal from the treatment chamber, said second carrier providing the coupling of each loaded cell carrier to the single source of controlled electric power. 

1. The method of vacuum dehydration, the steps of providing cell carriers for receiving the material to be dehydrated said cell carriers having a plurality of spaced vertical transverse electrically conductive and resistive rigid plates which when energized become the heat source with electrically conductive spacers therebetween, producing a controlled source of heat uniformly over the entire surface of each plate and uniformly with respect to all other plates of said cell carrier, loading the material to be dehydrated in said cell carrier between the plates and in contact therewith, placing and sealing the loaded cell carrier in a vacuum chamber, establishing a vacuum of 100 to 1,000 microns of mercury in said chamber, and simultaneously removing the water vapor at an accelerated rate while passing an electric current through the said cell plates to provide a heat source uniformly over the entire surfaces of each plate of the cell carrier.
 2. The method of claim 1 wherein the heating is controlled by establishing an electrical resistance in the plates to produce an electrical heat source of less than 3 watts per square inch with an input of 25 volts uniformly over both surfaces of each vertical plate, to reduce the water content in the material to be dehydrated to 1 to 4 percent in the final product.
 3. The method of claim 1 wherein a plurality of loaded cell carriers are placed in a single chamber, and wherein all cell carriers are connected to a single source of controlled electric power when positioned within said chamber, and energizing said plates for a uniform heating source with respect to both surfaces of all plates simultaneously and continuously.
 4. The method of claim 1 wherein the heating source plates of each cell carrier are connected in parallel so that when the loaded cell carriers are connected to a single source of controlled electric power the heating source is simultaneous and uniform over the entire plate areas for each plate in each of the cell carriers.
 5. The method of claim 1 wherein the sensible heat input of the heat source plates is less than the calculated requirements to accomplish dehydration in the product to a water content of 1 to 5 percent.
 6. The method of claim 1 wherein the plurality of loaded cell carriers are arranged in a second carrier for transportation to, treatment in, and removal from the treatment chamber, said second carrier providing the coupling of each loaded cell carrier to the single source of controlled electric power. 